Saturday, January 16, 2016

Using formulae

We have already seen that Equation: km = 1.6 times miles and Equation: C = pi times d are examples of formulae. There are many others that we use regularly in other subjects. Sometimes we have to construct our own formula:

Example

taxis
A taxi firm charges Equation: pounds 0.50 per mile plus a fixed charge of Equation: pounds 2.00 . Write down a formula for the cost Equation: C of hiring this taxi to travel Equation: n miles.

Solution

  • It costs Equation: pounds 2 + pounds 0.50 to travel Equation: 1 mile.
  • It costs Equation: pounds 2 + 2 times pounds 0.50 to travel Equation: 2 miles.
  • It costs Equation: pounds 2 + 3 times pounds 0.50 to travel Equation: 3 miles.
So travelling for Equation: n miles will cost Equation: pounds 2 + n times pounds 0.50 .
The formula is Equation: C = pounds 2 + (n times pounds 0.50) .
Note: Equation: pounds 0.50 = 50p .
QQuestion
A rectangle has a width of Equation: x and a length of Equation: 2x .
Diagram of a rectangle with the values 2x and x
Write down a formula for the perimeter Equation: P in terms of Equation: x .



Equation: P = 2x + x + 2x + x
Did you remember to include all Equation: 4 sides?
So Equation: P = 6x

Algebra

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